1. Field of the Invention
The present invention relates generally to an apparatus for processing semiconductor wafers and, more particularly, relates to a wafer boat assembly used to hold semiconductor wafers or the like within externally excited, chemical reaction systems wherein the reactant material flows over the wafers or workpieces which are held with their broad surfaces in perpendicular to the flow of the reactant material.
2. Description of the Prior Art
Plasma enhanced chemical vapor reactors are known in the art wherein the plasma reactant gas or gasses flow perpendicular to the broad surfaces of serially arranged workpieces. For instance, U.S. Pat. No. 4,401,507 issued to George M. Engle et al on Aug. 30, 1983, which is expressly incorporated herein by reference made thereto, is representative of the type of plasma chemical vapor reactor to which the present invention is applicable. The chemical reactor systems of the type disclosed in the U.S. Pat. No. 4,401,507, utilize an evacuable envelope retained in a furnace. A boat assembly that is removably inserted into the tabular envelope is used to hold workpieces perpendicular to the flow of the gas reactants that are passed through the tabular envelope during the deposition process onto the workpieces. Process uniformity is a great concern and ultimate goal in chemical vapor reactor systems. It is desirable to deposit a substantially uniform thickness of the film deposited onto the workpieces. Ideally, the film thickness on the workpieces processed in the chemical reactors should have a maximum of .+-.3% deviation wafer to wafer from one end of the loaded boat assembly to the other. In addition, it is desirable to be able to process as many workpieces as possible during each chemical vapor deposition process to maximize wafer throughput.
U.S. Pat. No. 4,610,748, issued to George M. Engle et al on Sept. 9, 1986 and entitled "Apparatus for Processing Semiconductor Wafers or the Like," which is also incorporated herein by reference made thereto, gives a detailed description of a boat assembly suitable for holding disc-shaped workpieces, such as semiconductor wafers, for processing in plasma enhanced chemical vapor reactors. While the boat assembly described in U.S. Pat. No. 4,610,748 represents a significant advance over known prior art, such a configuration is capable of improvement with respect to ease of disassembly for component replacement, assembly distortion during temperature excursions and component interchangeability between different sized assemblies used in diverse applications. It is also desirable to make a positive and reliable electrical contact to the electrode plates which support the workpieces. It is further very desirable to have a boat assembly which minimizes particulate contamination during processing.
Thus a need exists for an improved apparatus capable of being utilized in contemporary plasma enhanced chemical vapor deposition reactors which maintain process uniformity deviations below .+-.3% while, at the same time, allowing greater wafer throughput than is presently possible with conventional boat assemblies.